The slow school of the ages, the gradual acquisitions of the past, the legacies of heredity count for nothing therefore in the Osmia's education. Without any novitiate on its own part or that of its forebears, the insect is versed straight away in the calling which it has to pursue; it possesses, inseparable from its nature, the qualities demanded by its craft: some which are invariable and belong to the domain of instinct; others, flexible, belonging to the province of discernment. To divide a free lodging into chambers by means of mud partitions; to fill those chambers with a heap of pollen-flour, with a few sups of honey in the central part where the egg is to lie; in short, to prepare board and lodging for the unknown, for a family which the mothers have never seen in the past and will never see in the future: this, in its essential features, is the function of the Osmia's instinct. Here, everything is harmoniously, inflexibly, permanently preordained; the insect has but to follow its blind impulse to attain the goal. But the free lodging offered by chance varies exceedingly in hygienic conditions, in shape and in capacity. Instinct, which does not choose, which does not contrive, would, if it were alone, leave the insect's existence in peril. To help her out of her predicament, in these complex circumstances, the Osmia possesses her little stock of discernment, which distinguishes between the dry and the wet, the solid and the fragile, the sheltered and the exposed; which recognizes the worth or the worthlessness of a site and knows how to sprinkle it with cells according to the size and shape of the space at disposal. Here, slight industrial variations are necessary and inevitable; and the insect excels in them without any apprenticeship, as the experiment with the native Osmia of the quarries has just proved. Animal resources have a certain elasticity, within narrow limits. What we learn from the animals' industry at a given moment is not always the full measure of their skill. They possess latent powers held in reserve for certain emergencies. Long generations can succeed one another without employing them; but, should some circumstance require it, suddenly those powers burst forth, free of any previous attempts, even as the spark potentially contained in the flint flashes forth independently of all preceding gleams. Could one who knew nothing of the Sparrow but her nest under the eaves suspect the ball-shaped nest at the top of a tree? Would one who knew nothing of the Osmia save her home in the Snail-shell expect to see her accept as her dwelling a stump of reed, a paper funnel, a glass tube? My neighbour the Sparrow, impulsively taking it into her head to leave the roof for the plane-tree, the Osmia of the quarries, rejecting her natal cabin, the spiral of the shell, for my cylinder, alike show us how sudden and spontaneous are the industrial variations of animals. CHAPTER 7. ECONOMY OF ENERGY.